The corrosion of copper and iron-bearing metallurgies in steam generation feedwaters has been the subject of increasing concern in those industries utilizing boilers. Consequently, the corrosion can result in reduced reliability, damage to the systems, loss of effectiveness and increased costs due to cleaning, unscheduled outages and replacement of equipment. Transport of copper corrosion products to other boiler surfaces can result in decreased heat transfer and subsequent loss of productivity. Copper deposition on less noble metal surfaces can further exacerbate corrosion problems by causing galvanic corrosion.
Copper corrosion in boiler feedwater systems is primarily caused by the presence of dissolved oxygen, carbon dioxide and ammonia. Even under optimum feedwater condition, low dissolved oxygen and controlled pH, copper oxides will be released as particulate oxides, soluble Cu(I)/Cu(II) and metallic copper species. Copper oxides can continually redeposit within a boiler system, leading to poor heat transfer and tube overheating.
Iron corrosion in boiler feedwater systems is a degradative electrochemical reaction of the metal with its environment. Simply stated, it is the reversion of refined metals to their natural state. When steel corrodes, the loss of metal may result in failure of the boiler wall causing shut down of that particular system.
The problems with corrosion are exacerbated during upset conditions such as low or high pH, high oxygen, chloride or sulfate concentrations. These corrosion problems become even more aggravated when further corrosion-inducing species are introduced into the boiler feedwater. Such species include microbiological growth biocides and oxidizing biocides.